As a brake device of a vehicle, there is known, for example, an electronically controlled Brake (ECB) as an electronically controlled brake which electrically controls a brake force applied by a brake device, that is, a brake hydraulic pressure supplied to a wheel cylinder which drives the brake device depending on an operation amount (a pedal stroke, a depression force, and the like) input from a brake pedal.
The ECB is configured to accumulate a hydraulic pressure which is increased by a pump in an accumulator, adjusts the hydraulic pressure in response to a brake requirement of a driver, and supplies the hydraulic pressure to wheel cylinders as a brake hydraulic pressure. That is, when the driver depresses a brake pedal, a master cylinder generates a hydraulic pressure depending on an operation amount of the brake pedal as well as a part of an operating oil flows into a stroke simulator, and the operation amount of the brake pedal is adjusted depending on a depression force of the brake pedal. In contrast, a brake ECU sets a target deceleration of a vehicle depending on a pedal stroke, determines brake forces applied to respective wheels, and applies predetermined hydraulic pressures from the accumulator to the respective wheel cylinders.
In the electronically controlled brake device, the operation amount (the pedal stroke, the depression force, and the like) input from the brake pedal must be detected with a high degree of accuracy. There are brake pedal operation amount detecting apparatuses described in the following Patent Documents 1 and 2 as conventional brake pedal operation amount detecting apparatuses.
An operation force relating signal output device described in Patent Document 1 is configured such that a turn member, which is rotated about an axis line orthogonal to an axis line of an input rod by a relative movement of a brake operation member and the input rod, is attached to the brake operation member, the brake operation member and the input rod are urged by an elastic member in a direction where they are away from each other in an axis direction of the input rod, and the signal output device, which is operated by the relative movement between the brake operation member and the input rod and outputs a signal relating to an operation force, is interposed between the brake operation member and the turn member. Further, a brake operation force detection device described in Patent Document 2 is disposed with a detector, which is relatively movably held by a device main body, and a load detector, which is mechanically cooperated with the detector and detects a load from the detector, and detects a brake operation force of a brake operation member operated by a driver, and the brake operation force detection device is provided with a nonlinear characteristic application unit which makes the ratio of an output of the load detector to a movement amount of the detector smaller in a state in which the movement amount of the detector is large than a state in which the movement amount of the detector is small.    Patent Document 1: Japanese Patent No. 3453507    Patent Document 2: Japanese Patent Application Laid-open No. 2001-018768